Jeremy Deaton writes for Nexus Media. You can follow him @deaton_jeremy. This story was published in partnership with Nexus Media, a syndicated newswire covering climate, energy, policy, art, and culture.

You may have heard about the hole in the ozone layer, which hovers over Antarctica. It’s shrunk over time thanks to policies that curbed the use of ozone-depleting chemicals. In the nearly 40 years that NASA has kept track, it has never been smaller. That’s the good news.

The bad news is that a separate hole in the ozone layer briefly opened up in the Arctic in March before closing in April, and climate change may be partly to blame.

This isn’t the first such rift to develop in the Arctic, but it is the largest. Scientists say that in March, a stratospheric polar vortex—a band of strong, frigid winds circling the pole—corralled chlorine and bromine from polluted air and chewed away at the ozone layer. Weather patterns triggered by climate change likely set the stage for the reaction.

“In those years when a vortex can spin and set itself up and be undisturbed, it’s getting colder and colder,” says Ross Salawitch, a climate scientist at the University of Maryland. Cold air strengthens polar vortexes, allowing them to deal more damage to the ozone layer, he says.

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The ozone layer recently thinned over the Arctic. Warmer colors indicate more ozone, while cooler colors indicate less ozone.NASA